Risk is the probability that harm, injury, or, in the context of this document, disease will occur. The foundation of any safety program is the use of control measures appropriate for the risk posed by the activities and the agents in use. To characterize their risk, microorganisms and clinical materials are assigned to one of four Biosafety Levels (BSLs). For each BSL there is a unique set of safety equipment, facility design features, and practices that will reduce the risk of laboratory-acquired infections.

Agents: defined and characterized strains of microorganisms not known to consistently cause disease in healthy adults e.g., B. subtilis, S. cerevesiae, non-pathogenic E. coli. Includes recombinant DNA activities using such non-pathogenic organisms as hosts for the expression of genes incorporated into bacterial plasmids or low risk viral vectors such as baculovirus or Adeno Associated Virus.

2.2.4 Biosafety Level 4 (BSL-4)
Organisms in this category are of such extremely high risk that only a handful of laboratories nationwide work at this level. No such facilities exist at the University.

2.2.6 Risk Assessment
Biosafety Level classifications are appropriate for typical laboratory operations. The Principal Investigator or laboratory director is responsible for implementing more (or less) stringent practices based on laboratory specific conditions. Such a decision is ultimately the result a risk assessment process that accounts for the following:

Pathogenicity - the ability of an organism to cause disease.

Virulence - the severity of disease.

Transmission route - parenteral, ingestion, mucous membrane exposure, or inhalation. The latter route is of the greatest concern which is why organisms such as M. tuberculosis require more stringent control than organisms that are transmitted via direct contact, e.g., HBV.